What is the common method of Pipeline Hydrostatic Testing?

 One of the most common methods of pipeline hydrostatic testing is pressure testing. During pressure testing, the pressure inside a pipeline is increased to the desired levels for a specified period of time. In some cases, water will spill into the air or pool on the ground for a short time. Hydrostatic testing is usually performed by raising the pressure on a pipeline segment, with personnel on foot and helicopter patrolling to observe the test. The pressures are monitored using sophisticated computer data programs.

Temperature-compensated calculation method for pipeline hydrostatic testing

In piping hydrostatic testing, the temperature-compensated calculation method is used to take temperature and pressure changes into account. This method takes into account the physical characteristics of each variable and certifies that pressure/volume changes are within acceptable limits. This method is essential when pipelines are placed underground since temperature variations must be compensated for. Below are the basic steps for temperature-compensated calculations.

A typical hydrostatic pressure test involves filling a pipe section with fluid and then pressurizing it to a pressure higher than the pipe is likely to experience in normal service. This pressure is maintained for a predetermined period of time. Pipelines are hydrostatically tested prior to being placed in service, and periodically during operation. Some hydrostatic pressure tests require the use of just pressure, while others include both pressure and temperature.

Pre-testing of ductile iron pipe with water

If you are planning to install a new water pipeline, you should have it hydrostatically tested. The test pressure should be 150 psi or more at the highest point. Moreover, the test must be conducted for at least two hours and must not vary by more than five psi during the test. Also, you must exclude air before testing the pipe, so open-air release vents or fire hydrants. Corporation cocks may also be used to expel air.

For proper installation, it is essential to follow the manufacturer's instructions. The pipe ends shall be lubricated with a gasket lubricant, preferably the type used for push-on joints. The spigot shall be centrally located inside the bell. Then, the pipe should be fitted with bolts. The bolts must be properly positioned. Then, the spigot and gasket shall be installed.

Post-test inspection with radiography or ultrasonics

A pipeline hydrostatic test is conducted by applying a pressure of approximately 1.25 times the design pressure to a cylinder. Once the cylinder is at this pressure, the system is held under pressure for a predetermined time, during which the pipe is visually inspected for defects. If any defects are detected, they are immediately corrected. However, some defects may be present in weld zones and can cause problems in the pipeline when it is in use for extended periods of time.

For piping systems that are counterweight-supported or spring-supported, the QC inspector must visually inspect every length to ensure that the entire system is leak-free. This includes weld joints and bolted connections. The duration of this process depends on the length and width of the system. For smaller piping systems, an hour's inspection time may be sufficient.

Limitations of hydrostatic testing

There are several limitations of pipeline hydrostatic testing. These include its inability to detect subcritical flaws, which require greater internal pressures to be detected. Because of these limitations, hydrostatic testing is not recommended for retesting existing systems. Additionally, hydrostatic pressure tests do not provide measurements of the expansion or contraction of localized thin areas. Still, hydrostatic testing is an important tool for ensuring the safety of pipelines and other pipeline-related equipment.

The main limitation of isolation and testing is its limited range. Many types of modern line pipes are capable of passing hydrostatic tests up to a maximum yield strength (SMYS), but a single piece will not always reach this value. This is because the average yield strength of an order of pipe is usually far higher than the minimum value specified. Only a small percentage of pieces will show yielding at 100% SMYS. This type of yielding does not damage the pipeline, it is a coating or its integrity.